1. Field of the Invention
This invention broadly relates in one aspect to strip lighting systems of a type comprising connectable unitary modular strip lighting assemblies, as employed to provide illumination in a wide variety of industrial, commercial, and consumer applications. In another broad aspect, the present invention relates to a current-regulating circuit for maintaining current draw of an electrical power-consuming device at a predetermined current consumption level, even when the voltage supplied to the device undergoes fluctuation or oscillation.
2. Description of the Related Art
Linear lighting systems of the type known in the art as strip lighting systems, have been in extensive conventional use.
One configurational type of such strip lighting systems comprise modular strip lighting units including an elongate casing, generally in the form of an extruded tubular housing of resilient, translucent or transparent material (e.g. plastic tubing). Within the extruded tubular housing is a sequence of spaced-apart bulbs or other light emitting sources (such as LEDs, incandescent bulbs, or other electroluminescent lamps) in series and/or parallel relationship with one another. Strip lighting units of such illumination systems are thus provided in a unitary modular form, with the respective lighting units being interconnectable with one another, in series and/or parallel relationship, to form multi-unit extended lighting system assemblies for illumination of a specific environment or locus.
Another structural type of strip lighting system comprises an electroluminescent lamp including a layer of electroluminescent phosphor material, e.g., a metal activated zinc sulfide, which is fixedly positioned by a polymer binder between two conductive layers. One of the conductive layers is transparent. In such assembly, the application of an alternating electric field across the conductors causes the phosphors to become excited and emit electrons in the visible light spectrum.
In parallel relationship arrangements of interconnected strip lighting units, means are provided for electrical communication of the illumination elements, usually disposed in serial relationship to one another in the interior of the housing of the strip lighting unit, with an exterior, and often remote, electrical (voltage) source, as well as with other strip lighting units. Such electrical communication is typically effected by means of positive and negative conduction paths within the strip lighting unit. The positive and negative conduction paths may be suitably coupled, e.g., co-linearly or coaxially, with an electrical connection line forming a connection between the positive and the negative conduction paths within the strip lighting unit. Multiple modular light strip units thereby form a complex circuit of individually serial light sources grouped into strips which are in parallel relation to one another (providing a so-called "series/parallel" arrangement of the light source elements in the illumination system).
In series relationship arrangements of interconnected strip lighting units, each unit includes a simple series of connected light sources. The connection of successive units in the array is also in series, thereby simply extending a single conduction path.
The resulting array of modular strip lighting unit(s) is disposed at a selected position in the specific environment or locus of use. For example, a length of the strip lighting assembly formed by an end-to-end series-connected plurality of strip lighting units, may be provided in a non-slip nosing structure extending across the front edges of steps of a staircase, or mounted along a handrail or at the intersection of a wall and the floor in a hallway, thereby defining a directional path or boundary demarcation means. Another example is the provision of an illuminated path provided along the aisle and exits of an aircraft in the event of an emergency. A wide variety of decorative and safety-enhancement uses for such strip lighting systems exists. Further, when the housings of the individual component strip lighting units in the assembly are of a deformable and flexible character, holding their shape and conformation as deformed, the resulting strip lighting assembly may advantageously be utilized in non-linear deployment applications, in which the "line" of the originally interconnected strip lighting modular units may be bent or deformed to a desired curvature or other non-linear conformation at the locus of use.
Although strip lighting systems of the aforementioned general type have been widely and successfully commercialized, such systems nonetheless suffer from various associated deficiencies which have limited their utility and applicability, as described more fully below.
Individual light source (illumination) elements in strip lighting systems are generally highly sensitive to variations of input voltage to the strip lighting modular unit containing such light source elements. In both parallel and the series arrangements of strip lighting units in multi-unit system arrays, the failure of individual light source elements (generating either short circuits or open circuits) cause unsatisfactory fluctuations in voltage across the remaining light sources, often of a sufficient magnitude to render the unit at least partially inoperative.
Open circuit failures in a series arrangement of strip lighting modules will break the circuit completely, and result in illumination failure.
In previous strip lighting system designs of the series/parallel type (which is the most popular), the provision of different numbers of multiple strip lighting units in respective (parallel) branches of the strip lighting system, in which each strip lighting unit is identically constructed in relation to the others in the system, and/or the provision of differently sized strip lighting units in the branches of the strip lighting system, results in differing numbers of light source elements in the respective branches, and causes a differing total resistivity to be present in the respective branches.
In the case where differently sized strip lighting units are provided, the longer length strip lighting units (with more light source elements) generally draw more current than the shorter length strip lighting units (with less light source elements) in a parallel relationship, and the longer length strip lighting units therefore generate more intense light than the shorter lengths of otherwise identically constructed strip lighting modular units.
Correspondingly, the provision of different numbers of multiple strip lighting units in respective (parallel) branches of the strip lighting system, in which each strip lighting unit is identically constructed in relation to the others in the system, provides branches containing different numbers of light source elements, and the branches containing the larger numbers of light source elements likewise draw more current than the branches containing smaller numbers of light source elements, and the former branches containing more light source elements therefore generate more intense light than the latter branches containing less light source elements.
U.S. Pat. No. 5,107,408 teaches one solution to this incompatibility problem, wherein during installation, and prior to operation, of a strip lighting system composed of modular assembly strip lighting elements, resistors of predetermined value are positioned in series with the light source elements of each individual modular strip lighting unit, to balance the voltage drop across each unit to a predetermined or selected voltage drop value. Such a passively (or statically) balanced strip lighting system, however, does not have the ability to maintain a constant voltage across each light source when either the true input voltage varies or when an individual light source element fails.
Accordingly, it would be a significant advance in the art, and is correspondingly an object of the present invention, to provide a strip lighting system, and modular strip lighting units therefor, which overcome the aforementioned deficiencies of the prior art.
More specifically, it is one object of the present invention to provide a strip lighting system which is operable to maintain substantially uniform brightness of illumination across the full extent of the lighting array comprising multiple light source elements, even when the input voltage to the strip lighting system experiences fluctuations or time variation in the magnitude of the voltage, and even when individual light source elements fail in the lighting array.
It is another object of the present invention to provide a strip lighting modular unit for such an array, with such uniform current draw and brightness characteristics.
It is a further object of the invention to provide a current draw and brightness control circuit having utility in such strip lighting systems and modular units therefor.
It is still another object of the present invention to provide a current draw control circuit which is usefully employed to control the current consumption of an electrical power consuming device.
Various other objects, advantages and improvements of the present invention will be more fully apparent from the ensuing disclosure and appended claims.